A pairing protocol is disclosed in International Patent Application WO 2009/014438. This document describes a method to enable two mobile terminals to establish each others identity. One mobile terminal is physically tapped (softly hit) against the other. Both terminals detect the tapping. The terminals send messages identifying themselves and providing information about the detected tapping. When it is determined that the information about the detected tapping of two terminals matches, acknowledgement messages are sent to the mobile terminals to establish the mutual identification.
This method has a problem in that not each relatively loud and short noise is a tick caused by tapping terminals together, where too many “false ticks” affect the ease and usefulness of such a “tap-to-pair” system.
Another problem is that discrimination of ticks from non-ticks, especially in noisy environments needs much processing capacity when implemented in conventional ways, where the processing capacity of (small) mobile terminals is restricted and, besides, the terminal's battery has a limited capacity.
EP 1978508 discloses a method of musical beat detection for Karaoke purposes, among others. A musical tune is composed on the basis of a measure of time, such as a bar and a beat. The bar and beat determine the musical rhythm. The document describes system for determining beat position time points in from audio wave files. It is proposed to detect beat positions from large instantaneous peaks in the time-series waveform. But since beat components cannot be extracted highly accurately from a time-series waveform, an alternative is disclosed wherein a spectrogram is computed using an FFT (Fast Fourier Transform) on the time-series waveform. The system considers portions of the spectrogram at which the power spectrum instantaneously changes significantly. These are assumed to be beat components of the rhythm, due to hitting a drum for example.
EP 1978508 notes that such a beat detection does not provide in accurate beat timing extraction. To improve the accuracy an alignment process is performed on the beat position information of a musical tune or musical tune portions expected to have an identical tempo in the extracted beat position information. Such musical tune portions may be selected based on the variance of beat timing. By realigning the time points according to the tempo more accurate positioning of the beat is realized.
Thus, in EP 1978508 initial coarse detection of beat position from audio data in the audio file is followed by further processing of the detected positions. EP 1978508 does not propose to process the audio data itself more thoroughly. EP 1978508 would not be considered for a pairing protocol, because one cannot expect users of mobile terminals against each other according to a musical rhythm that lasts long enough to provide for a musical tune portion expected to have an identical tempo.